Alona cf. guttata Sars, 1862

Sinev, Artem Y. & Silva-Briano, Marcelo, 2012, Cladocerans of genus Alona Baird, 1843 (Cladocera: Anomopoda: Chydoridae) and related genera from Aguascalientes State, Mexico, Zootaxa 3569, pp. 1-24 : 15-19

Alona cf. guttata Sars, 1862

( Figs 8–10 )

Studied material: 3 parthenogenetic females from Pond near Laguna Seca pond. San Josй de Gracia, Aguascalientes, 25.09.1993, AYS; 6 parthenogenetic females from La Araña dam. Sierra Fría, San Josй de Gracia, Aguascalientes. 29.09.1993, AYS; 2 parthenogenetic females from small pool near the curtain of El Jocoqui dam, San Josй de Gracia, Aguascalientes, 25.02.2001, AYS; 10 parthenogenetic females from Pond 1, 2.5 Kms north of La Congoja town. San Josй de Grácia, Aguascalientes. 16.03.1991, AYS.

Description. Parthenogenetic female. General. In lateral view body ( Figs. 8 A–C, 9A–B) regular oval, of moderate height, maximum height at middle of body, in adults height/length ratio 0.67–0.70. Dorsal margin uniformly curved; postero-dorsal and postero-ventral angles broadly rounded; posterior margin uniformly curved; ventral margin almost straight; antero-ventral angle rounded. Body moderately compressed laterally. Valves oblique or with weakly developed tubercules in some specimens. Ventral margin with about 30–35 setae, anterior ten setae short, not forming separate group, distal setae of moderate length ( Fig. 8 D). Postero-dorsal angle ( Figs. 8 E, 9C) bears about 70 short, thin, hair-like setules of similar length, not organized in groups. A row of about 80 thin setules along the posterior margin on inner side of valve.

Head of moderate size, triangle-round in lateral view, rostrum short, pointing downward. Eye larger than ocellus. Distance from tip of rostrum to ocellus in adults slightly greater than that between ocellus and eye. Head shield with maximum width behind mandibular articulation, without any sculpture; rostrum short, broadly rounded; posterior margin of head shield broadly rounded. Three connected major head pores, middle pore smaller than other, PP about 0.5 IP ( Figs. 8 F, 9D). Lateral head pores minute, located about 1.0–1.2 IP distance from midline, at the level between anterior and middle major head pores. Labrum ( Figs. 8 G–H) of moderate size; labral keel narrow (height about 2 width), with rounded apex; anterior margin of keel convex, posterior margin with two clusters of short setules.

Thorax 2 times longer than abdomen, dorsal surface of abdominal segments not saddle-shaped.

Postabdomen ( Figs. 8 I–J, 9E) short, of moderate width, truncated with prominent distal angle, length about 2.5 height. Ventral margin straight. Base of claws separated from distal margin by clear incision. Distal margin straight; distal angle prominent, protruding before the base of claw, acute with rounded tip. Dorsal margin with distal part 1.6–1.7 times longer than preanal one, with postanal portion 1.3–1.5 times shorter than anal. Postanal portion of distal margin straight, anal portion weakly concave. Preanal angle well-defined, protruding, postanal angle weakly defined. 6–8 well-developed marginal denticles, decreasing in size basally and with three-four groups of marginal setules on anal margin. Each denticle with 3–6 spinules anteriorly, length of distal denticles exceed width of the postabdominal claw base. Eight-nine lateral fascicles of setules, six-seven distalmost fascicles wide, with longest setae in the middle, slightly shorter than longest marginal denticles. Several additional fascicles above the main row in anal portion. Postabdominal claw of moderate length, slightly longer than preanal portion of postabdomen. Basal spine about 0.2 of length of claw.

Antenna I ( Fig. 8 L) of moderate size, length about 2.5 width, with three clusters of long thin setules at anterior face. Antennal sensory seta slender, two times shorter than antenna I, arising almost at the middle of antenna. Nine terminal aesthetascs, two longest of them about 2/3 length of antennule.

Antenna II ( Figs. 8 K, 9F) relatively short. Antennal formula, setae 0–0–3/1–1–3, spines 1–0–1/0–0–1. Basal segment robust, branches of moderate length and width, basal segments of both branches 1.5 times longer than others. Seta arising from basal segment of endopodite thin, not reaching the end of endopodite. Seta arising from middle segment of endopodite of similar size with apical setae. Spine on basal segment of exopodite slightly shorter than middle segment. Apical spines slightly shorter than apical segments.

Six pairs of thoracic limbs. Limb I ( Figs. 10A–B ) of moderate size. Epipodite ovoid with a long process two times longer than exopodite itself. Accessory seta about 1/3 length of ODL seta. ODL with a long naked seta. IDL with three setae and two-three clusters of small setules, setae 2 and 3 only slightly shorter than ODL seta, armed with thin setules in distal part, seta 1 very short. Endite 3 with four setae of similar size. Endite 2 with three setae (d–f), setae f very long, 1.5 times longer than ODL seta. Endite 1 with two 2-segmented setae, both setulated in distal part, without a flat seta (I) shifted to limb base. No anterior naked setae found on endites 1–2. Six rows of thin long setules on ventral face of limb. Two long, slender ejector hooks, one of them larger than the other. Maxillar process elongated, with a short seta.

Limb II ( Fig. 10C ). Exopodite elongated, supplied with a single setulated seta of about 2/3 length of exopodite. Eight scraping setae (1–8), armed with spinules of similar shape, increasing in length distally. Distal armature of gnathobase with four elements. Filter plate with seven setae, the posteriormost two times shorter than others.

Limb III ( Figs. 10D–F ). Epipodite oval; exopodite subrectangular, with seven setae. Seta 3 being longest, setae 1, 4 and 6 about 1/3, 1/3 and 2/3 length of seta 3, respectively; other setae short. Setae 6–7 naked, all other setae plumose. Distal endite with three setae, two distalmost members slender, sharp, with distal parts unilaterally armed with sharp denticles; basalmost seta shorter, bilaterally armed with setules. Basal endite with four stiff setae, increasing in size toward the base, a small sensillum near the base of distalmost seta. Four soft setae increasing in size basally (a–d). Gnathobase not clearly separated from basal endite. Distal armature of gnathobase with four elements: an elongated, cylindrical sensillum; thin, bent seta; other two sharp spines. Filter plate III with seven setae.

Limb IV ( Figs. 10G–H ). Preepipodite setulated, epipodite with process two times longer than exopodite itself. Exopodite rounded, with six setae. Seta 3 longest, setae 1–2 slightly shorter than seta 3, setae 4, 5 and 6 of 1/3, 2/3 and 1/2 length of seta 3, respectively. Setae 1–4 plumose, seta 5 with short thick setules unilaterally, seta 6 naked. Inner-distal portion of limb IV with four setae and small cylindrical sensillum, seta 1 slender,sharp, with long denticles, first flaming-torch seta (2) broad, with 5–7 thick setules, two other thin, slender, with thin hair-like setules. Three soft setae of similar size. Gnathobase with a 2-segmented seta, and a small hillock distally. Filter plate with five setae.

Limb V ( Fig. 10I ). Preepipodite setulated, epipodite with process two times longer than exopodite itself. Exopodite divided into two lobes, incursion between lobes very deep, with four plumose setae, decreasing in size basally, seta 4 long, only 1.5 times shorter than seta 1. Inner limb portion, an oval lobe, with setulated inner margin. At inner face, two setae, one equal in length to seta 1 of exopodite, other 1.5 times shorter. Filter plate with three setae, large triangular sensillum located near it.

Limb VI ( Fig. 10J ) as elongated rounded lobe with setulated margin, length about 2 widths.

Ephippial females and males were not found.

Size. In single studied juvenile female of instar I, length is 0.21 mm, height 0.13 mm; in juvenile females of instar II, length 0.25–0.27 mm, height 0.16–0.19 mm; in adult female length 0.31–0.38 mm, height 0.21–0.25 mm.

Comments. The guttata -group is one of poorly studied groups of Alona s. lato. Alona guttata Sars, 1862 was described from Norway. Presently, A. guttata is reported worldwide, but identity between Palearctic populations and populations from other regions is strongly questioned (Van Damme & Eggermont, 2011). The second species of the group, A. barbulata , was described from USA, and is similar to A. guttata in many features ( Megard, 1967). A. barbulata differs from A. guttata by the shape of head shield and postabdomen, which has almost right, not prominent distal angle (see Megard 1967). Morphology of limbs of A. barbulata remains unknown, and its close relationship with A. guttata , presumed by Megard (1967), is not confirmed. The third species of this group is Palearctic A. werestschagini Sinev, 1999 , it clearly differs from A. guttata by the greater size and by the postabdomen morphology, but have similar appendages (see Sinev 1999).

Studied populations from Mexico are similar to A. guttata s. str. instead of A. barbulata , since they have postabdomen with a prominent, acute distal angles. We found no significant differences between studied specimens and those from Europe ( Alonso, 1996; Hudec 2010). Unfortunately, a full redescription of A. guttata was never conducted. Frequently, sibling-species of Chydoridae from different continents have no significant differences in the morphology of parthenogentic females, but clearly differ by that of the males (see Frey, 1985; Sinev 1998, 2009a; Sinev & Atroschenko, 2011). We expect that studied populations are not conspecific to the Palearctic A. guttata s. str., but the level of study of the latter does not allow us to verify this thesis. The problem can be solved after a study of gamogenetic specimens or genetic studies.

Distribution. In Aguascalientes, this species is found in the North-West region of the state, within the area of temperate climate, at the altitude 2000–3100 m.a.s.l., and not present in area with dry-hot climate. Such distribution suggests that the studied populations are conspecific to the populations of A. cf. gutatta from USA and Canada.

Figures

FIGURE 8. Alona cf. guttata Sars, 1862 from Pond 1, 2.5 Kms north of La Congoja town, San Josй de Gracia, Aguascalientes State, Mexico. A – B, juvenile females of instars I and II. C – L, parthenogenetic female. C, lateral view. D – E, antero-ventral and posteroventral corners of valves. F, head pores. G – H, labrum. I – J, postabdomen. K, antennule. L, antenna. Scale bars denote 0.1 mm for A – C, 0.05 for D – L.

FIGURE 9. Alona cf. guttata Sars, 1862 from a small pool near the curtain of El Jocoqui dam, San Josй de Gracia, Aguascalientes State, Mexico, parthenogentic female. A, lateral view. B, dorsal view. C, posteroventral corner of valves. D, head pores. E, postabdomen. F, antennule.

FIGURE 10. A – J, Alona cf. guttata Sars, 1862 from Pond 1, 2.5 Kms north of La Congoja town, San Josй de Gracia, Aguascalientes State, Mexico, parthenogenetic female. A, limb I. B, IDL and ODL of limb I. C, limb II. D, exopodite of limb III. E – F, inner portion of limb III. G, exopodite of limb IV. H, inner portion of limb IV. I, limb V. J, limb VI. K – M, Alona ossiani Sinev, 1998 from Pond 4 at Mesa Montoro mountain, Calvillo, Aguascalientes State, Mexico, parthenogenetic female. K, lateral view. L, head pores. M, postabdomen. Scale bars denote 0.2 mm for K, 0.1 mm for L – M, 0.05 for A – J.